Lord of the Rings: The Return of the King - He Loses It, He has It, Now He Doesn't Have It

When Frodo is leaving Shelob's lair, he get stuck in one of Shelob's webs. He then uses his sword Sting to cut himself out. Once he cuts himself out, he leaves his sword in the web. When he comes out of Shelob's lair, he still has his sword (its attached to his belt). Then after Frodo is attacked by Gollum, Frodo's sword is not on him like it should be.

Well the idea is Sam finds Sting and picks it up along with the elven vial, using them later to attack Shelob. I havent actually watched it but I suspect that the other comment was right and it was just his sheath.